How was this old "no hands pushup" viral video made?

Probably a shovel in the frozen ground up his pantleg. You can see him shift his weight to his right side when he goes hands free.

Yup probably exposed rebar up a pant leg or two, good catch

Edit: yup, you can see the bar sticking up in the back of his pants and he's trying to hide it, it's fed up through the right side pant leg